Various techniques for replacing the existing environment in containers for food product and other atmospheric sensitive products, such as some electronic devices or reactive metals are known in the art. Various methods exist for removing oxygen in food filling processes. Such processes are used, for example, in the packaging of nuts, coffee, powdered milk, cheese puffs, infant formula, beverages and various other types of food product. Typically, food containers are exposed to a inert gas flush and/or vacuum for a period of time, subsequent to filling but prior to sealing. The product may also be flushed with a inert gas prior to filling, or may be flushed after the filling process. When the oxygen has been substantially removed from the food contents therein, the containers are sealed, with or without vacuum.
A gas flushing apparatus for removing oxygen from food containers is disclosed in U.S. Pat. No. 4,140,159, issued to Domke. A conveyor belt carries the open top containers in a direction of movement directly below a gas flushing device. The gas flushing device supplies inert gas to the containers in two ways. First, a layer or blanket of low velocity flushing gas is supplied to the entire region immediately above and including the open tops of the containers through a distributing plate having a plurality of small openings. Second, each container is purged using a high velocity flushing gas jet supplied through a plurality of larger jet openings arranged side-by-side in a direction perpendicular to the direction of movement of the food containers. As the containers move forward, in the direction of movement, the steps of inert gas blanketing followed by jet flushing can be repeated a number of times until sufficient oxygen has been removed from the containers, and from the food contents therein.
One aspect of the apparatus disclosed in Domke is that the flow of gas in a container is constantly changing. The high velocity streams are directed through perpendicular openings in a plate, which creates eddies near the openings causing turbulence which may pull in outside air. Similarly, plate openings oriented perpendicular to the direction of the moving containers is disclosed in U.S. Pat. No. 2,630,958 to Hohl. As a container moves past the perpendicular row of high velocity jets, the jets are initially directed downward into the container at the leading edge of the container open top. As the container moves further forward, the flushing gas is directed into the center and, later, into the trailing edge of the open top, after which the container clears the row of jets before being exposed to the next perpendicular row of jets. The process is repeated as the container passes below the next row of jets.
The apparatus disclosed in Domke is directed at flushing empty containers and, in effect, relies mainly on a dilution process to decrease oxygen levels. One perpendicular row of jets per container pitch is inadequate to efficiently remove air contained in food product.
Constantly changing jet patterns in prior art devices create turbulence above and within the containers, which can cause surrounding air to be pulled into the containers by the jets. This turbulence also imposes a limitation on the speed at which the containers pass below the jets. As the containers move faster beneath the jets, the flow patterns within the containers change faster, and the turbulence increases. Also, at high line speeds, purging gas has more difficulty going down into the containers because of the relatively shorter residence time in contact with each high velocity row. The purging gas also has a greater tendency to remain in the headspace above the containers. In addition, a perpendicular arrangement of jets relative to the direction of container travel causes much of the jet to be directed outside the containers, especially when the containers are round. Moreover, the spacing apart of the perpendicular rows may further vary the flow pattern and pull outside air into the containers.
Attempts have also been made to remove oxygen from the headspace of containers. One such flushing device is disclosed in U.S. Pat. No. 5,452,563, issued to Marano et al. One problem with this device is that it requires large quantities of inert gas to reduce the oxygen levels to less than one percent. Preferably, the Marano device may require inert gas of at least 60 times the headspace volume of a filled milk carton, or seven times the volume of an empty carton to reduce the oxygen content to less than one percent. These inefficiencies may be caused in part by the design of Marano device which provides a hood with a 1 inch diameter circular opening to allow gas to flow into the containers moving along a conveyer. As with Domke, a sustained optimal flow pattern cannot be achieved and maintained with this design because the flow pattern is constantly being altered by the position of the container as it moves under the circular opening. The design also provides for a recessed area formed in the hood which acts to trap inert gas and exiting gas within the recessed area. This design will also slow the exit of gas from the container, and thus must rely in part on dilution to achieve its reduced oxygen levels. Accordingly, the Marano design which is directed toward using a high volume of inert gas to cover the entire container opening alters an optimal flow pattern that would efficiently sweep the oxygen from the container. Moreover, the large volumes of purging gases required by this process, which may include carbon dioxide, may violate OSHA requirements and present health problems.
Some other existing gassing systems require the gassing system to move with the container, and may require contact with the container. These systems require moving parts which leads to substantial maintenance and various other safety and operational problems.
It would be desirable to have an efficient gassing system to replace the existing atmospheric environment within empty or filled containers. It would also be desirable to have a system without moving parts that would be easy and efficient to maintain and operate. It would also be desirable to have a system to collect the gases exiting the containers as they are flushed.